1. Field of the Invention
The present invention relates to focus adjusting apparatuses and focus adjusting methods. Particularly, the present invention relates to automatic focus adjusting techniques.
2. Description of the Related Art
Conventionally, in a case where automatic focusing (AF) is performed in electronic still cameras and video cameras, a method is used, in which a lens position at which a high frequency component of a luminance signal supplied from an image-pickup element, such as CCD (Charge Coupled Device), is maximum is treated as an in-focus position. The following scan method is known as such a method. In the scan method, an evaluation value (focus evaluation value) calculated based on the high frequency component of the luminance signal obtained from the image-pickup element is successively stored while the lens is driven over its entire move range, and the lens position at which the thus-stored evaluation value exhibits the maximum is treated as the in-focus position.
In another method, a lens continues to be moved in such a direction that the focus evaluation value increases. This method is known as the hill climbing method (also referred to as continuous AF hereinafter).
Further, Japanese Patent No. 4,106,485 discloses the following method. In this method, the continuous AF is executed prior to instructions for image-taking preparation operation to maintain an in-focus state, thereby restricting the move range of a focus lens to be moved by the AF scan method for performing the image-taking preparation operation subsequent to instructions therefor. Thus, the AF operation time is decreased.
In the continuous AF, in a case where the lens is to be moved in such a direction that the focus evaluation value increases, focusing cannot be executed on an object to be focused unless an area to be focused is identified or determined in an image plane.
In the method of the above Japanese Patent, the above scan method is combined with the continuous AF to speedily perform the focusing operation. However, identification is not performed with respect to an object (principal object) to be focused in the image plane, on which a user wants to focus. Therefore, there is a possibility that focusing cannot be executed on an object to be focused, depending on the condition of an image-taking scene.